This is not really a step by step “How to”……its more of a “How I did it..but it might not work for you”

I cant find anyone who has done this conversion before me…So I think that I am the first !!

If you are thinking about doing this……You should probably have already done the L99 to LS3 conversion..not sure how or if its even possible to do this on a TRUE L99 car.

My car started life as an L99 car, but I did the LS3 conversion when I swapped out to a stroker 427 engine. My car is HIGHLY modified from stock, my engine / transmission wiring harness have been MAJORLY MODIFIED. Meaning that I have lengthened, shortened, and even removed un-necessary wiring from my engine harness before I ever imagined doing this project. So keep this in mind as you look at my pictures and writeup.
I am hoping that this will be a “guideline” to help others like myself that want a manual 6 speed transmission in place of the factory automatic.

As I am writing this…I still have a few “quirks” that haven’t been completely worked out yet… mainly stuff dealing with the BCM (body control module) because it still thinks the car is an automatic. I will explain this later.

Most of my parts were bought used from a Camaro5 member that swapped to a 4L80e automatic for racing. You can save a ton of money if you can find the right deal.

If you wanted to do this with new GM parts… here is the parts list with the part numbers:

Now you are ready to install the 6 speed manual transmission. And again…I wont go through all the steps, I am sure there is another DIY on here of how to do that also (look for how to install a new clutch) ..but basically install:

Now we are to the major stuff that makes this work in a factory auto car:

Pedals:

Its easiest to remove your driver seat first. Then remove factory Automatic brake pedal assembly. If I remember correctly, there are 4 nuts to the firewall, a bolt and clip for the brake rod, and a wiring connector to remove the assembly.
Removing all of this gives you a little extra room to install the clutch pedal assembly.

It might help to look at a friends 6 speed car to get an idea of how it looks and take measurements if you can.
Grab the pedal assembly and put it up under the dash, look up on the big metal structure and you can see where there are 2 threaded holes that mount the top part of the clutch pedal bracket assembly. I think it uses 10mm bolts ( I had some lying around from another project). Line your bracket assembly up with those holes and you can see where the studs will go through the firewall. Now move the assembly back out of the car. Make a template to drill with by using the gasket from the clutch pedal bracket to firewall as a pattern. Now tape it to the firewall on the inside and drill the 2 mounting holes and the center hole. This is probably the WORST part of this swap other than the wiring.

Once again, this part sucks…upside down on top of your head trying to drill just sucks..but it will all be worth it. Take your time and it will look almost factory.

While we are inside the car, let me mention this about the console / shifter assembly stuff.

The factory automatic console plate will work with the new shifter and boot. , but if you are very picky about things looking just right like I am, then you will notice if you bolt down the shifter boot in the factory location that when you pop back on the console plate that there is about a Ό inch gap at the front that just doesn’t look quite right. But if you move the boot a Ό of an inch forward and let the bolts just barely catch the plastic on the rear, and no need for the front 2 bolts at all…. it will hold just fine and when you pop the console plate back down everything looks perfect.

One more thing while we are inside the car…..

There is one more issue that we need to take car of while inside.
If you haven’t already noticed, your key is going to be stuck inside the ignition switch and not let you have it back.
Easy fix.
Unscrew and pop off the plastic that surrounds the steering column.
Look around where the ignition switch is. There is a plunger type solenoid that is attached to the ignition switch. Put your key into the ignition, turn to the “on” position , now turn it back and try to take the key out. it wont come out. now push the plunger towards the switch and the key comes right out.
So…take a zip-tie and put it around the little arm so that the arm is always toward the ignition switch. So that your key will always come out. this will make more sense when you see it for yourself.

This may seem kind of “redneck engineering” but it works fine and sometimes the best solution is down and dirty like this. If I later find another way, I will update this part.

Install your clutch fluid line from the clutch master down to the trans. install your clutch fluid reservoir and hose to the clutch master. Bleed the clutch. Install the transmission cooler lines and fill the transmission with fluid if you haven’t already.
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Wiring:

Now we are at the part that most people don’t like.

My car already had such a heavily modified engine / transmission wiring harness I did mine a little different.
So with that being said…this is just a guess that this will even work for you. (still assuming you have already done the “LS3 conversion” that deletes AFM and VVT)

I would remove the entire L99 wiring harness from the car and install the LS3 harness.

Then have a shop (or individual) with EFI Live, HP Tuners or something similar load a stock file from a factory manual transmission car into your computer. Making sure to turn off the “clutch position sensor” stuff so that the car will crank (because you do not have the wiring for the computer to see that the clutch is pushed in to crank)

Here is how I did mine….

But like I said mine was a “special case” and I think mine was actually harder to do that it would be for a car that is closer to stock with only an LS3 conversion.

I removed my engine / transmission harness from the car.
I then stripped all the tape and plastic wrap off so that it was only wires. Using wiring diagrams from Alldata.com, I started at the transmission connector and traced each and every wire back up to the connectors at the computer and fuse box locations. Then I unpinned each wire that had anything to do with the transmission from the connectors and made notes along the way.

Then I did the same thing to the new LS3 harness.

Then I took all the transmission wiring that I removed for the LS3 harness and pinned back into my connectors by the wiring diagrams. I also compared the 2 harnesses and found a few more wires that were different and moved those into my harness.

Once that was finished and installed back into the car, I uploaded a manual transmission car file using my HpTuners and the car cranked right up.

Wow thats awesome! I didnt think anyone would actaully do it because everyone said it would be super expensive. Do you mind giving a ball park figure of how much it costs to do this? The one thing I regret about my car is that it is auto...

I will be posting this in the Market within a few days - but have a complete TR6060 stock (just pulled for a 4L80e). It is from my 45th - exceptional shape - and less than 7000 miles on it.

I also have it equipped with an MGW Self Centering Shifter Mechanism (this is beyond the best of the best shifter mechanism) - and a Hurst Pistol Grip.

I have the stock Clutch (great shape) and will throw in a McCleod RXT twin because disk (3000.00 clutch) at no extra cost because it has some use on it - but would install it in a second, and was using it without issue.

Let me know if reading here and interested and will consider offers, not trying to get rich, but plan to post in the market and eBay this weekend. I will ship on palette my 4L80e came in but clearly local would be fantastic. I am in Louisville KY.

My 2 cents - M6 is the way to go it's just not for the strip. If I had my way it would have remained in the car and loved it.